1. The Field of the Invention
This invention relates to a proportioning flow control for controlling brine release from a membrane cartridge, as in a reverse osmosis system.
2. The Prior Art
In U.S. Pat. No. 4,077,883 issued Mar. 7, 1978, there is disclosed apparatus for controlling the flow of brine from a pressure resistant vessel containing a semipermeable membrane cartridge, as employed in a reverse osmosis system. The apparatus comprises an elongated small diameter duct formed of two portions. The open ends of these two small diameter duct portions are enclosed in a common compartment contained within the pressure resistant vessel and which is connected through a relief valve to means for collecting and storing permeate from the semipermeable membrane cartridge, under elevated pressure.
This arrangement functions well to control brine flow as well as controlling the permeate storage pressure, but assembly of the components has been laborious and expensive and location within the pressure resistant vessel requires disassembly of this vessel for any required flow control servicing. A flow control device which could be arranged outside of, or separate from, the pressure resistant vessel containing the membrane cartridge would be advantageous to provide a more accessible device but could result in sealing problems not encountered in the apparatus of U.S. Pat. 4,077,883. This occurs because the compartment of U.S. Pat. No. 4,007,883 operates with an internal pressure lower than the external pressure to which it is exposed within the pressure resistant container. Therefore any slight in-leakage will automatically pass out through the drain connection from the compartment. Leakage from a flow control located outside or separate from the pressure resistant vessel, however, may result in external dripping and formation of water pools in the area in which the system is installed.
Choice of material for the tubing from which the small diameter duct portions are fabricated may cause additional difficulties. Plastics, such as fluorinated hydrocarbons, which are capable of being drawn into tubing of excellent physical properties and uniformity, retain a slick or slippery surface to which sealants and adhesives will not ordinarily readily bond.
A simple proportioning flow control, with adequate sealing for use outside or separate from the pressure resistant vessel would be advantageous.